Printing method

ABSTRACT

A method of printing is disclosed wherein a latent image is first formed on a recording medium and thereafter developed by applying a toning liquid to the recording medium. The toning liquid is applied to the recording medium by forming a flow of liquid relative to the moving recording medium which thereby creates a meniscus in contact with only one face of the recording medium. The recording medium is guided in a curved elongated path at the point of application of the toning liquid.

United States Patent 11 1 Borelli et a1.

1 1 PRINTING METHOD [75] Inventors: Ronald F. Borelli, Medfield; DonaldJ. Gar-and, Chelmsford, both of Mass.

[73] Assignee: Honeywell Inc., Minneapolis, Minn. [22] Filed: June 8,1972 21 Appl. No.: 261,121

Related US. Application Data [62] Division of Ser. No. 888,769, Dec. 29,1969, Pat. No.

[58] Field of Search 117/37 LE, 115; 118/637, 118/DIG. 23; 96/1 R, 1 LY,1.2

1451 Oct. 1, 1974 3,368,526 2/1968 Matsumoto et a1 118/637 3,369,9182/1968 Young 117/37 LE 3,416,493 12/1968 Robinson et a1.. 118/6373,420,151 1/1969 Levine et a1. 355/4 3,462,286 8/1969 Geest et a1117/115 3,526,536 9/1970 Spencos et al.... 117/115 3,527,684 9/1970 Yorket a1 117/37 LE 3,576,623 4/1971 96/1 LY 3,583,806 6/1971 355/43,613,701 10/1971 Ando 134/64 3,701,337 10/1972 Borelli et a1. 117/37 LEFOREIGN PATENTS OR APPLICATIONS 1,578,391 8/1919 France 118/637 PrimaryExaminer-Michael Sofocleous Attorney, Agent, or FirmRona1d T. Reiling;William F. White [57] ABSTRACT A method of printing is disclosed whereina latent 156] References Cited image is first formed on a recordingmedium and UNITED STATES PATENTS thereafter developed by applying atoning liquid to the 2,877,133 3/1959 Mayer 117/37 LE recording mediumThe toning liquid is pp to the 2,925,312 2/1960 Hollman 96/1 R recordingmedium by forming a flow of liquid relative 3,094,914 6/ 1963 Smith95/89 to the moving recording medium which thereby cre- 5 /1964 Clark eta1 118/637 ates a meniscus in contact with only one face of the3,169,887 2/1965 118/637 recording medium. The recording medium isguided in 32421902 3/1966 118/637 a curved elongated path at the pointof application of 3,270,637 9/1966 96/1 R the toning liquid 3,276,89610/1966 Fisher 117/37 LE 3,301,675 1/1967 Fauser et a1. 96/1.2 5 Claims,4 Drawing Figures A DRIVE CONTROL 1 BRAKING MEANS Emmm' mm 3,839,071

DRIVE CONTROL BRAKING MEANS Fig: 2.

PRINTING METHOD This is a division, of application Ser. No. 888,769,filed Dec. 29, I969. now U.S. Pat. No. 3,7()l,337, issued on Oct. 31,1972.

BACKGROUND OF THE INVENTION This invention relates to methods and meansfor printing upon a recording medium and particularly to methods andmeans for printing permanent images electrographically upon a papermedium at high speeds.

Such high speed printing is desirable in environments such as a computerprint-out. Generally electrographic printing, is accomplished upon anelectrographic paper medium composed of a conductively treated paperbase that supports a plastic dielectric coating. The paper medium ispositioned between an electrode that contacts the conductive base and aand a second electrode whose surface conforms to the shapes to beprinted. A high voltage applied between the two electrodes'excites thepaper medium and establishes an electrostatic field across thedielectric coating. The coating retains a residual electrostatic fieldthat constitutes a charged latent image of the shapes to be printed.

The latent image is developed by subjecting the paper medium to a toningliquid composed of charged resin particles which are softened by aliquid carrier. The residual electrostatic field at the dielectricsurface attracts these particles and holds them. This makes the imagevisible. The image is then fixed, i.e., made permanent, by drying toremoving the liquid carrier. This solidifies the particles and bondsthem to the paper. Such drying may be done by heating.

The toning liquid used to develop the latent image consist of thesecharged toning particles and the solvent liquid carrier. Normally, inthe process, large amounts of this carrier liquid are left on and in thepaper medium. This liquid is volatile and when the paper is dried forexpelled the developed image large amounts of fumes are expedded intothe local environment. Large amounts of such fumes are unpleasant andpossibly harmful. Attempts to reduce these fumes to acceptable levels byreducing the amount of liquid carrier used to hold the particles havenot met with success. Poor images resulted. Moreover, large amounts ofliquid require long time periods to vaporize. These place a limit on theprinting speed. Where high speed is essential, such as in the read outof a computer, such printing systems have been inadequate.

SUMMARY OF THE INVENTION The invention obviates these deficiencies.According to a feature of the invention only one face of the medium,preferably the dielectric face, is covered with toning liquid. Accordingto another feature this is done by guiding the medium through alongitudinally curved path, and into a controlled flow of toning liquidthat encounters only one face of the medium. Preferably the flow isformed by liquid moving means that discharge a continuous downwardlaminar flow of the liquid over an inclined surface near the path.Drying means then need eliminate only this liquid. Since only a plasticdielectric face need be wetted by the liquid and liquid is not absorbedby a paper base the amount of volatile fumes are created by drying aresubstantially reduced.

According to another feature of the invention the flow is tangential tothe curved path.

According to another feature of the invention the inclined surface formsa gap with the guide means at the curved path. The size of the gap issufficiently small so that when the medium moves through the gap, andthe liquid flows through the gap, the liquid forms a continuous meniscusover the portion of the curved path closest to the inclined surface.

According to another feature of the invention, control means control theflow of toning liquid over the inclined surface. Preferably, thesecontrol means respond to driving means that transport the recordingmedium.

According to yet another feature of the invention, valve means controlthe flow of the liquid from one of several reservoirs carrying differentcolors of the liquid so as to pass one color of liquid over the inclinedsurface.

According to still another feature of the invention the guide meansinclude a roller extending transversely to the longitudinal direction ofthe movement of the medium and the driving means apply a longitudinalforce on the medium so that there exist a continuous normal force overthe arc against the roller. The normal force assures uniformdistribution of the flowing liquid. It also prevents any liquid fromentering the side of the medium contacting the roller.

According to still another feature of the invention, the gap issufficiently small so the carrier medium contacts the liquid, butsufficiently large to keep the liquid in contact with only one side ofthe medium.

According to another feature the guide means and inclined surface aremade of conductive materials. These align the residual electrostaticfield lines, that form the image on the medium. Preferably, the gap issmall enough to make these lines perpendicular to the opposing faces ofthe guide means and the surface.

According to still another feature of the invention, the liquid movingmeans include nozzle means for spreading the liquid over the inclinedsurface to distribute it so as to encounter the entire transversedimension of the medium at the meniscus in the gap.

According to still another feature of the invention, the gap size issuch and the flow such that the moving medium shears a portion of theliquid off the meniscus and the flow replaces the portion to retain themeniscus. Preferably, the flow and movement of the medium are in thesame direction.

These and other features of the invention are pointed out in the claims.Other objects and advantages of the invention will become obvious fromthe following detailed description when read in light of the followingdrawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of aprinting system embodying features of the invention;

FIG. 2 is a cross-sectional view of the recording medium in FIG. 1;

FIG. 3 is a sectional view of the medium passing through the meniscus inFIG. 1; and

FIG. 4 is a cross-sectional view of the medium passing through thedrying rolls of FIG. I.

DESCRIPTION OF PREFERRED EMBODIMENT In FIG. I, a pair of peripherallyengaging elastomeric capstan rolls I and 12 rotating as shown pinch aweb of electrographic paper 14 and draw it from a supply roll 16 uponwhich the paper is wound. A cross section of the paper 14 appears inFIG. 2. The paper is composed of a conductively treated paper-fibrousbase 18 which supports a plastic dielectric coating 20. The paper isrolled on the roll 16 so as to place the coating 20 on the inside. Thepaper 14 constitutes the recording medium. It is referred to as paperalthough only a portion is composed of paper fibers. The base 18 may forexample be 0.003 inch thick and the coating 0.0005 inch thick.

Braking means 17 places the paper 14 under longitudinal tension as thecapstan rolls l0 and 12 pull it. This keeps the paper taut. The bearingsin roll 16 may exhibit sufficient friction to constitute the brakingmeans 17.

The paper 14 leaving the supply roll 16 passes over an idler roll 22with the dielectric coating 20 contacing the roll. An excitation station23 then excites the paper 14. In the excitation station 23 the paper 14passes between the peripheral surface of an idling image roll 24 whichcontacts the coating 20 and an electrode 26 which is biased tofrictionally contact the conductive base 18. The periphery of the roll24 maybe etched so as to project outwardly to form the pattern ofwriting which is to be printed on the paper. It may also be composed ofvariable projecting types that are controlled by a computer to produce acomputer print-out. Essentially the writing makes the image roll 24 aprint roll.

A 700 volt direct current source 28 applies an excitation voltagebetween the electrode 26 and the image roll 24 which is grounded. Thisforms an electrostatic field across the coating 20 at those portions ofthe periphery on the roll 24 that project and contact the layer 20 andthe conductive base 18. The image roll 24 rotates as the paper 14 passesbetween it and the electrode 26. The roll 24 and the electrode 26 areslightly less wide than the width of the paper 14. The coating 20retains across it a residual electrostatic field corre sponding to theexciting field and the image on the periphery of the image roll 24. Thisconstitutes a latent image.

The paper 14 emerging from between the roll 24 and electrode 26 passesover an exit idler roll 30 and around a steel toning roll 32 of adeveloping or toning station 34. The roll 32 guides the paper and ispreferably as narrow or slightly narrower than the paper. The plasticcoating 20 of the paper 14 faces outwardly of the toning roll 32. Sincethe capstan rolls l0 and 12 draw the paper 14 against the restrainingforce at the supply roll 16, the longitudinal forces on the paperproduce radial forces directed inwardly to the axis of the roll 32. Thisassures substantially firm contact between the roll 32 and the base 18of the paper 14.

During this process the dielectric coating 20 of the paper 14 continuesto retain across its thickness the latent electrostatic field thatconstitutes the latent image ofthe projections on the periphery of theimage roll 24. In order to develop this latent image, a pump 36 drives atoning liquid. The latter comprises a high resistance carrier such askerosene, which has a resistance of ohms per cubic centimeter, and asuspension of charged colored thermoplastic resin particles which formthe printing materialv The pump 36 drives this fluid 38 through aflexible pipe 40 to a fan nozzle 42. The latter spreads the fluidlaterally over a flat steel in clined plate 44 to form a shallow laminarliquid flow. The plate is as narrow or narrower than the width of thepaper. The plate 44 is spaced from the freely turning toning roll 32 soas to form a gap 46 between the coating 20 and the plate 44 of from0.005 inch to 0.020 inch. When the liquid 38 flows through the gap 46,it contacts the coating 20 and forms a meniscus 48. The meniscus appearsmore particularly in FIG. 3 which shows an enlarged cross section of theroll 32, the paper 14, the plate 44, the meniscus 48 and the liquid 38in FIG. 1.

As stated the toning liquid 38 flows by gravity to the toning area whereit contacts the paper 14 due to the closeness of the roller 32 and theflat plate 44. As the liquid 38 contacts the paper 14, the meniscus 48is formed at the coating 20. The meniscus is formed and kept intact bythe forces of adhesion between the molecules of the flowing liquid 38and the coating 20 of the paper 14. It extends transversely across theroll 32 and clings peripherally from one side of the gap. at itsnarrowest portion, to the other. The gap 46 is sufficiently small toform such a meniscus but large enough to allow some passage of toningliquid 38.

The thermoplastic resin particles suspended in the kerosene of theliquid 38 are charged and adhere to the portions of the surface 20 whichare oppositely charged. This makes the image visible. As the paper 14 isdrawn away from the capstan rolls l0 and 12 it shears off the topportion of the meniscus 48 and retains a portion of the liquid and thethermoplastic resin particles. The flow that supports the meniscus ismaintained by the constant pumping action of the pump 36. The flow isadjusted so the paper 14 just contacts or kisses" the liquid. This helpsassure even distribution of the liquid and a distribution of theparticles that depends almost exclusively on the electrostatic field. Auniformly developed image results.

The particles continue to adhere to the now wet surface of the coating20. A wiper 50 in the shape of a longitudinally notched rod removes someof the liquid 38 on the dielectric coating. The remaining liquid 38flowing out of the meniscus 48 is caught in a trough 52 and fed back toa selected one of three reservoirs 54, 56 and 58 containing toner liquidof different colors.

The liquid 38 in each reservoir 54, 56 and 58 has suspended thereinthermoplastic resin particles of differ ent colors so as to print indifferent colors. Six pairs of electrically actuated flow valves 60, 62,64, 66, 68, and select which of the fluids 38 are drawn by the pump 36from their respective reservoirs. The valves 60-70 are arranged so thattwo pairs are closed and one pair open to fluid flow.

The tightness of the paper about the roll 32 helps assure uniformdistribution of liquid over the coating 20. It also keeps liquid 38 fromthe meniscus 48 from entering between the roll 32 and base 18 of thepaper 14. Such entry would cause the base to absorb a good deal of theliquid and make drying difficult. The particles in the liquid on thecoating are concentrated in those areas carrying the electrostaticfield.

The steel roll 32 and the steel plate 44 are in close proximity acrossthe gap. In the vicinity of the gap they thus tend to align the residualelectrostatic field across the dielectric to be substantiallyperpendicular to the dielectric. Such alignment prevents fringing. Itassures a sharp visible image. It prevents fuzziness that fringing mayintroduce. The smaller the gap the sharper the image.

An idler roll 71 directs the paper into a drying apparatus 72 where theimage is fixed. In this drying appara tus the paper passes between anelastomeric back-up roll 74 that contacts the base of the paper 14 and asecond elastomeric absorption roll 76 that contacts the wettoner-carrying coating 20 of the paper 14. Both of the rolls idle andmove with paper 14. Mountings 77 that support rolls 74 and 76 bias therolls to apply pressure against the paper 14.

As the paper passes through the rolls 74 and 76 compress not only thepaper but a portion of the peripheral surface of the elastomericmaterial. The elastomeric material of the absorption roll 76 is such asto be absorbent of the liquid 38. As the roll 76 has its peripherycompressed near the engagement point with the roll 74, any air in theabsorptive surface or any other fluid in the absorptive surface issqueezed out. As the paper passes through and emerges between the pinchof the rolls, the portion of the roll 76 that has been compressed beginsto expand and absorb the kerosene carrier in the liquid 38 on thesurface of the coating 20 of the paper 14. Those particles which areattracted by their electrophoretic condition to the charged portions ofthe coating 20 remain on and in the crevices of the coating 20.

The concentration of charged particles near the charged portions of thecoating 20 develops the printing to create the visible image. Theremoval of the surrounding liquid 38 produces printing upon the paper 14and fixes the paper. However, the concentration when squeezed may alsotransfer a portion of the image onto the roll 76. This may then betransferred to a successive portion of the moving paper. To preventthis, a rotating cleaning brush 78 that dips into a cleaning fluid 80 ofa trough 82 applies the cleaning fluid to the surface of the elastomerroller 76. This removes any image.

A scraper 84 compresses the surface of the roll 76 after its contactwith the brush 78. The scraper 84 squeezes the surface of theelastomeric roll between itself and the axis of the roll. This squeezesout any toning liquid or cleaning fluid that may exist in the absorptivepores of the roll 76. At the same time it scrapes the toning liquid andcleaning fluid that was on the surface of the roll and that which wassqueezed out of the roll. This substantially dries the paper 14. Thepaper then passes between the capstan rolls 10 and 12 and out to autilizing station. The scraper avoids the effect of a squeeze rollerwhich would, as it turns, reapply the liquid squeezed out.

A drive control 85 that senses the speed of the capstan rolls 10controls the flow of the pump 36 so that more or less fluid 38 can passout the nozzle 42 in dependence upon the speed of the paper 14. In thatmanner, if the paper speed 14 at the gap 46 is so fast as to shear offlarge amounts of liquid in the meniscus 48 in a short period of time,sufflcient fluid is provided to replace the liquid in the meniscus. Thispermits a variable speed printer that can achieve high speeds. The highspeeds are rendered possible because large amounts of liquid can beconcentrated along a thin line across the moving paper. The line can beconstantly replenished.

By virtue of the invention a controlled amount of toning liquid 38 issupplied to only one surface of the paper 14 at any one time. The amountof liquid applied can be controlled by controlling the flow down theplate 44 on the basis of the speed with which the paper moves and shearsoff the liquid. Moreover, because the roll 32 is round and because thecapstan rolls l0 and 12 and the braking means 17 place a longitudinalforce on the carrier, a normal force exist throughout the arc over whichthe paper contacts the guide roll 32. This force causes the paper to hugthe guide roll 32 across the arc. Thus, even distribution of liquid isencouraged. Also, liquid is discouraged from entering the portionbetween the toning roll 32 and the dielectric 20 and wetting theflberous base 18 of the paper 14. This limits the absorption of liquid.It prevents needless vapors.

The steel roll 32 and plate 44 separated by a narrow gap 46 assure asharp developed image by aligning the electrostatic field linesperpendicularly to the surface of dielectric 20 at the gap 46.

It should be noted that the thickness of the paper 14 is somewhatexaggerated for clarity throughout the drawings.

The diameter of the roll 32 is between one-half inch and 3 inches andpreferably 1 inch. Other sizes may of course be used.

While an embodiment of the invention has been described in detail itwill be obvious to those skilled in the art that the invention may beotherwise embodied within its spirit and scope.

What is claimed is:

1. A method of printing on a flat flexible moving recording mediumhaving opposing faces comprising the steps of:

exciting the moving recording medium so as to form a latentelectrostatic image onto the recording medium; applying a toning liquidto the excited recording medium containing the latent electrostaticimage to develop the latent electrostatic image, said step of applyingthe toning liquid including the steps of:

guiding the moving recording medium along a longitudinally curved path,forming a continuous flow of toning liquid along a surface spaced fromthe longitudinally curved path, wherein the spaced surface is aninclined flat plane so that the flow of liquid is inclined relative tothe longitudinally curved path, so as to cause a liquid to flow througha gap between the spaced surface and the longitudinally curved path, and

controlling the continuous flow of the toning liquid by sensing thespeed with which the recording medium is being moved so as to controlthe flow of fluid in response to the speed with which the recordingmedium is being moved so as to create a single meniscus sufflcientlylarge to wet the recording medium on only one face as the recordingmedium moves through the gap between the spaced surface and thelongitudinally curved path and shears off the meniscus, and

removing excess liquid from the recording medium.

2. The method as in claim 1 further comprising selectively and singlypassing toning liquids of different colors over the spaced surface.

3. The method as in claim 1 wherein '7 8 the recording medium is anelongated strip moving in statically charge the dielectric coating so asto form a longitudinal path while it is being sensitized, dea latentelectrostatic image. veloped and while the toning liquid is being re- 5.The method of claim 4 wherein the step of removmoved. ing the excessliquid further comprises the steps of:

4. The method of claim 1 wherein the recording me- 5 squeezing therecording medium between an absordium is composed of a fibrous basecoated with a dibent roll and a second roll with the dielectric layerelectric and wherein said step of exciting the recording in contact withthe absorbent roll; and medium comprises the step of: compressing andscraping the liquid out of the absorsensitizing the recording medium byapplying a voltbent roll.

age across the recording medium so as to electro-

1. A METHOD OF PRINTING ON A FLAT-FLEXIBLE MOVING RECORDING MEDIUMHAVING OPPOSING FACES COMPRISING THE STEPS OF: EXCITING THE MOVINGRECORDING MEDIUM SO AS TO FORM A LATENT ELECTROSTATIC IMAGE ONTO THERECORDING MEDIUM; APPLYING A TONING LIQUID TO THE EXCITED RECORDING AMEDIUM CONTAINING THE LATENT ELECTROSTATIC IMAGE TO DEVELOP THE LATENTELECTROSATIC IMAGE, SAID STEP OF APPLYING THE TONING LIQUID INCLUDINGTHE STEPS OF: GUIDING THE MOVING RECORDING MEDIUM ALONG A LONGITUDINALLYCURVED PATH, FORMING A CONTINOUS FLOW OF TONING LIQUID ALONG A SURFACESPACED FROM THE LONGITUDINALLY CURVED PATH, WHEREIN THE SPACED SURFACEIS AN INCLINED FLAT PLANE SO THAT THE FLOW OF LIQUID IS INCLINEDRELATIVE TO THE LONGITUDINALLY CURVED PATH, SO AS TO CAUSE A LIQUID TOFLOW THROUGH A GAP BETWEEN THE SPACED SURFACE AND THE LONGITUDINALLYCURVED PATH, AND CONTROLLING THE CONTINOUS FLOW OF THE TONING LIQUID BYSENSING THE SPEED WITH WHICH THE RECORDING MEDIUM IS BEING MOVED SO ASTO CONTROL THE FLOW FLUID IN RESPONSE TO THE SPEED WITH WHICH THERECORDING MEDIUM IS BEING MOVED SO AS TO CREATE A SINGLE MENISCUSSUFFICIENTLY LARGE TO WET THE RECORDING MEDIUM ON ONLY ONE FACE AS THERECORDING MEDIUM MOVES THROUGH THE GAP BETWEEN THE SPACED SURFACES ANDTHE LONGITUDINALLY CURVED PATH AND SHEARS OFF THE MENISCUS, AND REMOVINGEXCESS LIQUID FROM THE RECORDING MEDIUM.
 2. The method as in claim 1further comprising selectively and singly passing toning liquids ofdifferent colors over the spaced surface.
 3. The method as in claim 1wherein the recording medium is an elongated strip moving in alongitudinal path while it is being sensitized, developed and while thetoning liquid is being removed.
 4. The method of claim 1 wherein therecording medium is composed of a fibrous base coated with a dielectricand wherein said step of exciting the recording medium comprises thestep of: sensitizing the recording medium by applying a voltage acrossthe recording medium so as to electrostatically charge the dielectriccoating so as to form a latent electrostatic image.
 5. The method ofclaim 4 wherein the step of removing the excess liquid further comprisesthe steps of: squeezing the recording medium between an absorbent rolland a second roll with the dielectric layer in contact with theabsorbent roll; and compressing and scraping the liquid out of theabsorbent roll.